A rotor assembly of the type used in axial flow turbines includes a rotor disk and a plurality of rotor blades extending radially outwardly from the disk. In such constructions, a flowpath for working medium gases extends axially through the rotor assembly and between the rotor blades of the rotor assembly.
Each rotor blade has an airfoil section which extends radially outwardly from the rotor assembly and into the working medium flowpath. The airfoil section adapts the blade to extract energy from the working medium gases for driving the rotor assembly about an axis of rotation. The rotor blade includes a root section which adapts the blade to engage a corresponding slot in the rotor disk. A platform section extends laterally from the blade and is disposed between the root section and the airfoil section to provide an inner boundary to the working medium flowpath.
As the rotor assembly is driven about the axis of rotation by the working medium gases, the gases interact with the rotor blades causing variations in the aerodynamic loading on the rotor blades. The variations in loading induce vibrations in the rotor blades. These vibrations, especially if they increase in magnitude, induce stresses in the rotor blades and adversely effect the fatigue life of the rotor blades.
One example of a construction which provides damping to the rotor blades and sealing to a cavity between adjacent rotor blades is shown in U.S. Pat. No.: 4,455,122 issued to Schwarzmann et al., entitled Blade to Blade Vibration Damper. In this construction, the adjacent blade platforms are separated over at least a portion of this axial length by a gap region. A damper is disposed against the underside of adjacent blade platform sections and a seal is spaced sufficiently close to the damper so as to engage the damper under centrifugal loads to augment damping of the rotor blades by the damper. The damper also blocks the flow of cooling air through the gap region between the adjacent platform sections. Other constructions are shown in U.S. Pat. No.: 3,318,573 issued to Matsuki et al., entitled Apparatus for Maintaining Rotor Disk of Gas Turbine Engine at a Low Temperature, U.S. Pat. No.: 3,709,631 issued to Karstensen et al., entitled Turbine Blade Seal Arrangement, and U.S. Patent No.: 4,872,812 issued to Hendley entitled Turbine Blade Platform Sealing and Vibration Damping Apparatus.
Still another embodiment is shown in U.S. Pat. No.: 3,834,831 issued to Mitchell entitled Blade Shank Cooling Arrangement. In Mitchell, the cavity between adjacent rotor blades is sealed by a plurality of cylindrical buffer segments 44 which may be disposed between the platforms to prevent movement of the blades towards each other and to permit the escape of cooling fluid therethrough.
The above art notwithstanding, scientists and engineers working under the direction of Applicant's assignee have sought to develop effective cooling schemes for supplying cooling air to the critical location between adjacent rotor blades in gas turbine engines.